Background-deflection Brillouin microscopy reveals altered biomechanics of intracellular stress granules by ALS protein FUS

Altered cellular biomechanics have been implicated as key photogenic triggers in age-related diseases. An aberrant liquid-to-solid phase transition, observed in in vitro reconstituted droplets of FUS protein, has been recently proposed as a possible pathogenic mechanism for amyotrophic lateral sclerosis (ALS). Whether such transition occurs in cell environments is currently unknown as a consequence of the limited measuring capability of the existing techniques, which are invasive or lack of subcellular resolution. Here we developed a non-contact and label-free imaging method, named background-deflection Brillouin microscopy, to investigate the three-dimensional intracellular biomechanics at a sub-micron resolution. Our method exploits diffraction to achieve an unprecedented 10,000-fold enhancement in the spectral contrast of single-stage spectrometers, enabling, to the best of our knowledge, the first direct biomechanical analysis on intracellular stress granules containing ALS mutant FUS protein in fixed cells. Our findings provide fundamental insights on the critical aggregation step underlying the neurodegenerative ALS disease

Brillouin Scattering Microscopy for Mechanical Imaging

In a world where science is constantly challenged to solve problems of increasing complexity, light is paving new ways to gather information about the physical properties of matter. Among these properties, elasticity is becoming fundamental in the understanding and the diagnosis of several diseases. Current solutions to gather mechanical information, however, measure the response of a material to an applied excitation, which makes them invasive and limited by a low spatial resolution. In contrast with these techniques, Brillouin spectroscopy offers the unique solution to retrieve stiffness information from the spectrum of the light scattered by inherent thermal acoustic waves. The combination of Brillouin spectroscopy with confocal microscopy has yielded a confocal Brillouin microscope able to perform mechanical imaging in a non-invasive manner. This was used to investigate two different biological problems: on the one hand the stiffness variations in specific endothelium cells of the eye, aiming at a better understanding of the mechanisms responsible for glaucoma, and on the other the characterisation of the mechanical structures of blood vessels, which could provide fundamental information regarding the formation of atherosclerotic plaques. Following an investigation on the optimal geometry that minimises the spectral broadening caused by the collection of photons over a range of scattering angles, high resolution Brillouin imaging was obtained in a confocal backscattering arrangement. To the best of our knowledge this thesis presents, for the first time, sub-cellular Brillouin images. In particular, in vitro Brillouin images of single HUVEC cells were acquired to investigate the cell’s mechanical response to the application of the Latrunculin-A drug. This analysis, together with the finding of a linear correlation between the Brillouin modulus and the standard Young’s modulus, validates the technique as a feasible means of measuring stiffness. Following this assessment, Brillouin images of normal and diseased vessels were acquired showing that the atherosclerotic plaques had a lower stiffness compared to both diseased and healthy vessel walls. These results might encourage the application of confocal Brillouin microscopy as the tool of choice for the investigation of the arterial biomechanics.Open Acces

Acoustic Source Localization by Fusing Distributed Microphone Arrays Measurements

Publication in the conference proceedings of EUSIPCO, Lausanne, Switzerland, 200

Diffraction-free light droplets for axially-resolved volume imaging

An ideal direct imaging system entails a method to illuminate on command a single diffraction-limited region in a generally thick and turbid volume. The best approximation to this is the use of large-aperture lenses that focus light into a spot. This strategy fails for regions that are embedded deep into the sample, where diffraction and scattering prevail. Airy beams and Bessel beams are solutions of the Helmholtz Equation that are both non-diffracting and self-healing, features that make them naturally able to outdo the effects of distance into the volume but intrinsically do not allow resolution along the propagation axis. Here, we demonstrate diffraction-free self-healing three-dimensional monochromatic light spots able to penetrate deep into the volume of a sample, resist against deflection in turbid environments, and offer axial resolution comparable to that of Gaussian beams. The fields, formed from coherent mixtures of Bessel beams, manifest a more than ten-fold increase in their undistorted penetration, even in turbid milk solutions, compared to diffraction-limited beams. In a fluorescence imaging scheme, we find a ten-fold increase in image contrast compared to diffraction-limited illuminations, and a constant axial resolution even after four Rayleigh lengths. Results pave the way to new opportunities in three-dimensional microscopy

Ultra-sensitive refractive index gas sensor with functionalized silicon nitride photonic circuits

Portable and cost-effective gas sensors are gaining demand for a number of environmental, biomedical, and industrial applications, yet current devices are confined into specialized labs and cannot be extended to general use. Here, we demonstrate a part-per-billion-sensitive refractive index gas sensor on a photonic chip based on silicon nitride waveguides functionalized with a mesoporous silica top-cladding layer. Low-concentration chemical vapors are detected by monitoring the output spectral pattern of an integrated unbalanced Mach-Zehnder interferometer having one coated arm exposed to the gas vapors. We retrieved a limit of detection of 65 ppb, 247 ppb, and 1.6 ppb for acetone, isopropyl alcohol, and ethanol, respectively. Our on-chip refractive index sensor provides, to the best of our knowledge, an unprecedented limit of detection for low gas concentrations based on photonic integrated circuits. As such, our results herald the implementation of compact, portable, and inexpensive devices for on-site and real-time environmental monitoring and medical diagnostics

Breaking the Contrast Limit in Single-Pass Fabry-Pérot Spectrometers

The development of high-resolution Fabry-Pérot interferometers has enabled a wide range of scientific and technological advances—ranging from the characterization of material properties to the more fundamental studies of quasi particles in condensed matter. Spectral contrast is key to measuring weak signals and can reach a 103 peak-to-background ratio in a single-pass assembly.At its heart, this limit is a consequence of an unbalanced field amplitude across multiple interfering paths, with an ensuing reduced fringe visibility. Using a high-resolution, high-throughput virtually imaged phased array spectrometer, we demonstrate an intensity-equalization method to achieve an unprecedented 1000-fold increase in spectral contrast in a single-stage, single-pass configuration. To validate the system, we obtain the Brillouin spectrum of water at high scattering concentrations where, unlike with the standard scheme, the inelastic peaks are highly resolved. Our method brings the interferometer close to its ultimate limits and allows rapid high-resolution spectral analysis in a wide range of fields, including Brillouin spectroscopy, mechanical imaging, and molecular fingerprinting

Facial scanning technologies in the era of digital workflow: A systematic review and network meta-analysis.

PURPOSE The aim of this network meta-analysis is to evaluate the accuracy of various face-scanning technologies in the market, with respect to the different dimensions of space (x, y, and z axes). Furthermore, attention will be paid to the type of technologies currently used and to the best practices for high-quality scan acquisition. MATERIAL AND METHODS The review was conducted following the PRISMA guidelines and its updates. A thorough search was performed using the digital databases MEDLINE, PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials by entering research lines or various combinations of free words. The main keywords used during the search process were "photogrammetry", "laser scanner", "optical scanner", "3D, and "face". RESULTS None of the included technologies significantly deviated from direct anthropometry. The obtained mean differences in the distances between the considered landmarks range from 1.10 to -1.74 mm. CONCLUSION Limiting the movements of the patient and scanner allows for more accurate facial scans with all the technologies involved. Active technologies such as laser scanners (LS), structured light (SL), and infrared structured light (ISL) have accuracy comparable to that of static stereophotogrammetry while being more cost-effective and less time-consuming

Quantification of plaque stiffness by Brillouin microscopy in experimental thin cap fibroatheroma

Plaques vulnerable to rupture are characterized by a thin and stiff fibrous cap overlaying a soft lipid-rich necrotic core. The ability to measure local plaque stiffness directly to quantify plaque stress and predict rupture potential would be very attractive, but no current technology does so. This study seeks to validate the use of Brillouin microscopy to measure the Brillouin frequency shift, which is related to stiffness, within vulnerable plaques. The left carotid artery of an ApoE-/- mouse was instrumented with a cuff that induced vulnerable plaque development in nine weeks. Adjacent histological sections from the instrumented and control arteries were stained for either lipids or collagen content, or imaged with confocal Brillouin microscopy. Mean Brillouin frequency shift was 15.79±0.09 GHz in the plaque compared with 16.24±0.15 (p \u3c 0.002) and 17.16±0.56 GHz (p \u3c 0.002) in the media of the diseased and control vessel sections, respectively. In addition, frequency shift exhibited a strong inverse correlation with lipid area of 20.67±0.06 (p \u3c 0.01) and strong direct correlation with collagen area of 0.71±0.15 (p \u3c 0.05). This is the first study, to the best of our knowledge, to apply Brillouin spectroscopy to quantify atherosclerotic plaque stiffness, which motivates combining this technology with intravascular imaging to improve detection of vulnerable plaques in patients